1. Field of the Invention
This invention is related to a method and apparatus for measuring ice amount of ice tank for ice-storage type air-conditioning system and in particular to one by which the amount of ice in the ice tank can be precisely calculated from the conductivity of the water in the ice tank as input data for energy management control system to improve the efficiency for the air-conditioning system.
2. Description of the Prior Art
There are two major types of ice making machine: ice-on coil type and dynamic harvest type. Conventional ice storage HVAC systems are ice-on coil type which uses a coil in ice tank to make ice. During ice producing process, ice is attached on the surface of the coil and the water level in ice tank is slightly increased with the amount of ice made. A liquid level sensor is employed as the ice inventory sensor for the coil-type ice maker.
Modern ice storage systems are dynamic type ice harvester. Ice water is pumped from the ice storage tank and distributed to a thin film surface of ice making plate in ice harvester above the ice tank and returned to the ice storage tank by gravity. When water temperature is low, some of the water is frozen into sheets of ice. Periodically, hot gas is injecting into ice making plate to melt a thin layer of ice slab. Ice is then released from ice harvester and dropped into ice tank.
The liquid level sensor for the conventional coil-type ice maker is not an adequate instrument to measure the amount of ice for dynamic ice harvester. The density of ice is 0.92. Hence, before all the water in ice tank is becoming ice, the ice slab or ice particle is floated on the water surface. The volume of ice underneath the water surface and the volume of water transformed into ice are equal. Water level will not change until ice has reached the bottom of the ice tank, and the liquid level sensor will not be able to distinguish half tank of ice from no ice.
So far, there is no adequate method to correctly measure the amount of ice in the ice tank for dynamic type ice harvest systems. The ice inventory in ice tank is an essentially important parameter for effective control of thermal storage management for large scaled HVAC industries.
Therefore, it is an object of the present invention to provide a method and apparatus for measuring ice amount of ice tank for ice-storage type air-conditioning system by which the amount of ice in the ice tank can be precisely calculated from the conductivity of the water in the ice tank as input data for energy management control system to improve the efficiency for the air-conditioning system.